Mediating Reductive Charge Shift Reactions in Electron Transport Chains

Abstract

We report the synthesis of a full-fledged family of covalent electron donor-acceptor-acceptor conjugates and their charge-transfer characterization by means of advanced photophysical assays. By virtue of variable excited state energies and electron donor strengths, either Zn(II)Porphyrins or Zn(II)Phthalocyanines were linked to different electron-transport chains featuring pairs of electron accepting fullerenes, that is, C and C. In this way, a fine-tuned redox gradient is established to power a unidirectional, long-range charge transport from the excited-state electron donor via a transient C toward C. This strategy helps minimize energy losses in the reductive, short-range charge shift from C to C. At the forefront of our investigations are excited-state dynamics deduced from femtosecond transient absorption spectroscopic measurements and subsequent computational deconvolution of the transient absorption spectra. These provide evidence for cascades of short-range charge-transfer processes, including reductive charge shift reactions between the two electron-accepting fullerenes, and for kinetics that are influenced by the nature and length of the respective spacer. Of key importance is the postulate of a mediating state in the charge-shift reaction at weak electronic couplings. Our results point to an intimate relationship between triplet-triplet energy transfer and charge transfer.

Synergy of Electrostatic and π–π Interactions in the Realization of Nanoscale Artificial Photosynthetic Model Systems

“…Moreover, their intense optical absorption in the red region of the solar spectrum renders them as excellent antennae. Such unique physicochemical properties have provided the incentive to incorporate Pcs into a large number of electron donor‐acceptor systems using both covalent and non‐covalent methodologies . The role of Pcs is to harvest light efficiently and, once photoexcited, to act as electron donors.…”

Controlling the Charge Transfer Mechanism and Efficiency by Means of Different C70 Regioisomeric Adducts

“…Interestingly, the extinction coefficients of DL1 and DL2 are significantly lower compared to the H 2 P reference, which is in line with previously reported porphyrin–fullerene electron donor–acceptor systems and prompts to electronic communication between the photo‐ and redox‐active constituents. [ 55 ]…”

Molecular engineering for high-performance fullerene broadband photodetectors

“…In this way, the excitons generated by light absorption are dissociated inside the molecules, and the generated carriers are also transported within the molecules, which fundamentally avoids the influence of phase separation between the donor and acceptor on the dissociation of excitons. [29][30][31][32][33][34][35] Porphyrin molecules are macrocyclic conjugated electron-rich compounds that can act as electron donors and exhibit strong absorption in the visible light region. 36,37 By contrast, fullerenes are electron-deficient molecules that can act as electron acceptors 38 and show strong absorption in UV region.…”